Weird lean condition I can't figure out

[chevota]

Now and then it commands a leaner than 1.00 Lambda while under load, and I can't figure it out. It doesn't happen often, but when it does the lambda varies between 1.1 to 1.7 lambda. It studders when it does this, and it's not a fuel cut feeling, but just like it looks, too lean. It's always about a half second after I give it gas, then it leans out for 1.5 to 2 seconds, then it's fine. It doesn't matter how much gas I give it, so it happens with just a little or it could be floored, but it only happens when I give it more gas.
Usually only one O2 sensor sees this lean mix, left or right which seems random. Today it did both, which also happens. The Desired Lambda and EQ Cmd command it lean, so it's not a fuel supply issue. It seems rpm, load and boost don't matter much either.

Another thing is it has only done this with three tunes, ever. If I load a new tune it goes away. I see nothing in common between the three tunes so I suspect that it may be a glitch because that does happen. The second tune it did this lean thing I decided to drive it for a while to see if I can figure out what is happening, but no luck. Over two weeks it only did it maybe ten times?
The only pattern I see is it almost always happens after being stuck behind a slow driver. You know, the 65 in the fast lane type. Once I get a shot to get around them, studder... Again, it's rare that it happens, but when it does, that's the condition. If I try to simulate it, it's a fail. Is that weird or what? So it would seem the existence and proximity of the inconsiderate a-hole appears to be affecting my car

Basically, how/why would it ever command lean under load? Anyone know? Anyone else had this happen?

Pix example from yesterday:
lean.jpg

[chevota]

This issue is happening more often as time passes. Now it does it several times a day and 1/4 to 1/2 throttle seems to trigger is most often. I should say 1/4 to 1/2 gas pedal, the throttle does whatever the hell it wants. It still refuses to do it when I try make it happen, and still greatly prefers it when passing an obstructing driver.
I've been running 50% Ethanol but changed to Gas for a couple months while trying to smog it, and it still did it.

Nobody has any idea or had the same happen? Just another one of my personal jinxes?

[chevota]

Probably the worst one yet. Lean for 3 seconds, peaking at 1.6 Lambda under 16 lbs boost at the 12:13:35 time stamp:

lean.hpl

Surprised it even ran, but I kept on it just to get data, then let off when it seemed it had no intention of recovering.
I see STFT goes to 0, which only happens when decelerating and is the only time Lambda is ever commanded leaner than 1.00.
Spark freezes too, which generally only happens on decel. So it gives me the impression it's going into decel mode?